Capacitor device, electronic parts packaging structure, and method of manufacturing the capacitor device

ABSTRACT

In a capacitor device of the present invention includes a substrate, a plurality of lower electrodes formed on the substrate, a plurality of dielectric films formed on a plurality of lower electrodes respectively in a state that the dielectric films are separated mutually, and upper electrodes formed on a plurality of dielectric films respectively, a plurality of capacitors each composed of the lower electrode, the dielectric film, and the upper electrode are arranged on the substrate respectively, and each of the dielectric films in a plurality of capacitors has a different film thickness.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a capacitor device, an electronic partspackaging structure, and a method of manufacturing the capacitor deviceand, more particularly, a capacitor device capable of being applied to adecoupling capacitor that is arranged on a circuit substrate on whichhigh-speed operated electronic parts are mounted to stabilize a powersupply voltage and also reduce a high-frequency noise, an electronicparts packaging structure in which such capacitor device is built, and amethod of manufacturing the capacitor device.

2. Description of the Related Art

In recent years, reduction in the power-supply voltage due to increasein a processing speed and reduction in power consumption is acceleratedin the digital LSIs including the microprocessor. In such digital LSIs,a power-supply voltage of the LSI is apt to become unstable when theimpedance of the LSI is suddenly varied, and so forth. Also, a stableoperation in a higher-frequency (GHz) range is required of high-speedoperated digital LSIS, and thus it is needed to prevent the malfunctionof the LSI due to the high-frequency noise.

Therefore, for the purpose of stabilizing the power-supply voltage andreducing the high-frequency noise, the decoupling capacitor is arrangedbetween a power-supply line and a ground line of the LSI.

For instance, in Patent Literature 1 (Patent Application Publication(KOKAI) 2001-110675) and Patent Literature 2 (Patent ApplicationPublication (KOKAI) 2002-260960), as the capacitor incorporated into theprinted wiring substrate, the capacitor utilizing the metal oxide filmobtained by applying the anodic oxidation to the valve metal such astantalum, or the like as the dielectric layer is set forth.

In the circuit substrate having the conventional decoupling capacitor,such capacitor is packaged onto the area of the circuit substrateadjacent to the area on which the LSI chip is packaged. In this case,since leads must be provided between the LSI chip and the capacitor, arelatively large inductance is present between these leads. Therefore,even though the decoupling capacitor is provided, an effect ofsuppressing a variation in the power-supply voltage applied to thehigh-speed operated electronic parts and also reducing thehigh-frequency noise is lessened.

As a result, the method of setting the wiring distance between the LSIchip and the capacitor to the shortest length by placing the decouplingcapacitor directly under the LSI chip to reduce the inductance isproposed.

However, there is a limit to the reduction in the parasitic inductanceeven though the wiring distance between the LSI chip and the capacitoris set to the shortest length. Then, when the higher frequency of theLSI is further forwarded, such a situation is supposed that either thepower-supply voltage of the LSI becomes unstable or the malfunction ofthe LSI is caused by the high-frequency noise. As a result, thedecoupling capacitor having the characteristic that its impedance isreduced over a wider frequency band is requested.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a capacitor devicecapable of being applied to a decoupling capacitor that can reduce animpedance in a wide frequency band and can be suited to a higherfrequency of electronic parts, an electronic parts packaging structurein which such capacitor device is built, and a method of manufacturingthe capacitor device.

The present invention is associated with a capacitor device thatcomprises a substrate; a plurality of lower electrodes formed on thesubstrate; a plurality of dielectric films formed on the plurality oflower electrodes respectively in a state that the dielectric films areseparated mutually; and upper electrodes formed on the plurality ofdielectric films respectively; wherein a plurality of capacitors eachcomposed of the lower electrode, the dielectric film, and the upperelectrode are arranged on the substrate respectively, and each of thedielectric films in the plurality of capacitors has a different filmthickness.

In the capacitor device of the present invention, a plurality ofcapacitors constructed by the lower electrode, the dielectric film, andthe upper electrode respectively are formed on the substrate as onechip. Then, the film thicknesses of respective dielectric films are setdifferently among a plurality of capacitors, and thus the electrostaticcapacities of respective capacitors are differentiated.

In the capacitor device of the present invention, a plurality ofcapacitors are connected in parallel between the power-supply line andthe ground line of the circuit substrate on which the high-speedoperated electronic parts are mounted, and this capacitor device acts asthe decoupling capacitor. Since the decoupling capacitor is constructedby connecting a plurality of capacitors each having the differentelectrostatic capacity in parallel, the resonance frequencies areshifted among a plurality of capacitors and therefore the impedance canbe reduced in a wide frequency band.

Meanwhile, the resonance frequency of the capacitor depends on not onlythe electrostatic capacity but also the inductance. However, in thecapacitor device of the present invention, since it is not needed thatthe basic structure of the capacitor such as the electrode area, and thelike is not changed, the inductance can be set identically amongrespective capacitors.

Therefore, when the electrical design is conducted to attain theimpedance reduction over a wide frequency band by adjusting theresonance frequencies of respective capacitors, there is no need to takethe change in the inductances of respective capacitors intoconsideration, and only the change in the electrostatic capacitiesshould be considered. In addition, since the resonance frequency of thecapacitor has such a characteristic that such resonance frequencychanges in inverse proportion to the electrostatic capacity, theelectrical design can be made extremely easy.

Also, the capacitor device of the present invention is constructed byforming a plurality of capacitors on the substrate as one chip.Therefore, a packaging cost can be reduced rather than the case where aplurality of capacitor parts having the different electrostatic capacityrespectively are packaged individually, and also such capacitor devicecan respond to the high-density packaging.

Further, reduction in thickness of the capacitor device can be attainedby reducing a thickness of the substrate, and in addition the capacitordevice of the present invention can be arranged directly under theelectronic parts. Therefore, the parasitic inductance can be reducedwidely.

Also, in one preferred mode of the present invention, respectivedielectric films of the capacitor device are made of the metal oxidefilm that is formed by applying the anodic oxidation to the valve metalfilm. In the case of this mode, first the valve metal film is formed onthe conductive film that is formed on the substrate. Then, the resistfilm in which the opening portions are provided in the predeterminedportions in the valve metal film is formed, and then the metal oxidefilm is formed by oxidizing the valve metal film exposed from theopening portions by virtue of the anodic oxidation. Then, the dielectricfilms each having the different dielectric film thickness are formed indifferent areas of the valve metal film by repeating this step whilechanging the conditions of the anodic oxidation. Then, the upperelectrodes are formed on the dielectric film, and then the lowerelectrodes are formed by patterning the valve metal film and theconductive film. As a result, a plurality of capacitors in which thefilm thickness of each dielectric film is different respectively areeasily formed on the substrate as one chip.

As described above, the capacitor device of the present invention hasthe small impedance in the wide frequency band. As a result, an effectof suppressing a variation in the power-supply voltage applied to thehigh-speed operated electronic parts and also reducing thehigh-frequency noise can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an equivalent circuit of a decouplingcapacitor in which a plurality of capacitors are connected in parallelbetween a power supply line and a ground line of a circuit board onwhich the load (LSI) is mounted;

FIG. 2 is a view showing the impedance characteristic of the decouplingcapacitor in FIG. 1;

FIGS. 3A to 3J are sectional views showing a method of manufacturing acapacitor device according to a first embodiment of the presentinvention;

FIG. 4 is a diagram showing an equivalent circuit when the capacitordevice according to the first embodiment of the present invention isapplied to the decoupling capacitor;

FIG. 5 is a view showing the impedance characteristics of the capacitordevice in FIG. 4;

FIG. 6 is a plan view showing a variation of the capacitor deviceaccording to the first embodiment of the present invention;

FIG. 7 is a sectional view showing the variation of the same capacitordevice;

FIGS. 8A to 8H are sectional views showing a method of manufacturing anelectronic parts packaging structure in which the capacitor deviceaccording to the first embodiment of the present invention is built; and

FIGS. 9A to 9C are sectional views showing a method of manufacturing acapacitor device according to a second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be explained with reference tothe accompanying drawings hereinafter.

Prior to explanation of a capacitor device according to embodiments ofthe present invention, the decoupling capacitor having the structurethat a plurality of capacitors are connected in parallel between thepower-supply line and the ground line of the circuit substrate on whichthe LSI chip is mounted will be explained hereunder. FIG. 1 is a diagramshowing an equivalent circuit of a decoupling capacitor in which aplurality of capacitors are connected in parallel between a power supplyline and a ground line of a circuit board on which the load (LSI) ismounted. FIG. 2 is a view showing the impedance characteristic of thedecoupling capacitor in FIG. 1.

Normally, the decoupling capacitor adapted for use with thehigh-performance LSI is requested to have the low impedance over a widerange from a low-frequency range to a high-frequency range. An exampleof the decoupling circuit taking account of such request is shown inFIG. 1. A first capacitor C₁, a second capacitor C₂, and a thirdcapacitor C₃ all having the same electrostatic capacity are connected inparallel between the power-supply line and the ground line (GND) of thecircuit substrate on which the load (LSI) is mounted.

The impedance characteristic of the individual capacitors (C₁, C₂, C₃)has the characteristic indicated by a solid line in FIG. 2. Then, theimpedance characteristic of the decoupling capacitor C₁,₂, ₃ constructedby connecting respective capacitors (C₁, C₂, C₃) in parallel isindicated by a chain line in FIG. 2. A frequency range X in which theimpedance of the decoupling capacitor C₁,₂,₃ is reduced smaller than 10m Ω or less becomes 90 to 180 MHz, and such decoupling capacitor has aneffect to reduce the impedance over a wide frequency band.

The electrostatic capacity of capacitors (C₁, C₂, C₃) at this time is 30nF (a sum of the electrostatic capacities is 90 nF) respectively. Anequivalent series resistance (ESR) is 10 m Ω respectively, and also anequivalent series inductance (ESL) is 50 pH respectively.

Also, it is known that, if the decoupling capacitor is constructed byconnecting in parallel a plurality of capacitors the electrostaticcapacities of which are mutually different, its impedance in a widefrequency band can be reduced further.

However, these capacitors C₁, C₂, C₃ are not manufactured as one chip,and the decoupling capacitor is constructed by packaging individualcapacitor parts. Therefore, not only an increase in packaging cost isbrought about but also it is difficult for the decoupling capacitor tobe adapted for use with the high-density packaging. Also, in the casewhere a plurality of capacitor parts whose electrostatic capacity ischanged by changing an electrode area are used, electrical design mustbe conducted with regard to the inductance as well as the electrostaticcapacity. Thus, the problem exists that the electrical design becomescomplicated.

The inventors of this application studied earnestly the decouplingcapacitor having the structure that makes the impedance reduction in theabove wide frequency band possible. As a result, the inventors of thisapplication found the fact that, if the electrostatic capacities aredifferentiated mutually by controlling a film thickness of thedielectric film of the capacitor without change of the inductance, notonly the decoupling capacitor can be manufactured as one chip to reducea packaging cost but also the impedance can be reduced in a widerfrequency band by an easy electrical design.

First Embodiment

Next, a capacitor device according to a first embodiment of the presentinvention will be explained hereunder. FIGS. 3A to 3J are sectionalviews showing a method of manufacturing a capacitor device according toa first embodiment of the present invention in sequence.

First, as shown in FIG. 3A, a core substrate 10 made of silicon, glass,ceramic, resin, or the like, or a metal such as iron-nickel alloy,aluminum, or the like is prepared. In the case where a resin substrateis used as the core substrate 10, it is preferable that the resincontaining fillers such as silica and having a coefficient of thermalexpansion of 5 to 30 ppm/K should be employed.

Also, when the thin-type capacitor device is manufactured, the coresubstrate 10 having a thickness of 50 μm or less is employed. When thethin-type core substrate 10 is employed, the core substrate may be fixedto the supporting member and then the supporting member may be removedafter manufacturing steps are ended. Alternately, the core substrate 10having a normal thickness is employed and then the back surface of thecore substrate 10 may be ground after the production of the capacitor isfinished.

Then, as shown in FIG. 3B, a conductive film 12 serving as a lowerelectrode of the capacitor and having a film thickness of about 10 μm,for example, is formed on the core substrate 10. A copper (Cu) isemployed as the material of the conductive film 12, for example, andsuch conductive film 12 is formed by the sputtering method, or the like.In this case, when a silicon substrate or a metal substrate is employedas the core substrate 10, an insulating film is formed on the coresubstrate and then the conductive film 12 is formed.

Then, as also shown in FIG. 3B, a first intermediate film 14 made oftitanium (Ti), aluminum (Al), or the like is formed on the conductivefilm 12. Then, a tantalum film (Ta film) 16 whose film thickness is 600nm, for example, is formed on the first intermediate film 14 by thesputtering method or the CVD method. The tantalum is an example of thevalve metal. Here, the “valve metal” signifies the metal having such aso-called valve action that its metal oxide obtained by applying theanodic oxidation passes an electric current therethrough only in onedirection but hardly passes the electric current therethrough in theopposite direction. As such valve metal, there are aluminum (Al),titanium (Ti), hafnium (Hf), niobium (Nb), zirconium (Zr), etc. inaddition to tantalum. In the present embodiment, the metal oxide filmobtained by selectively oxidizing the valve metal film is employed asthe dielectric film of the capacitor.

Then, as shown in FIG. 3C, a first resist film 18 in which an openingportion 18 x is provided in its portion, in which a first dielectricfilm of a first capacitor is formed, on the tantalum film 16 is formedby the photolithography.

Then, the portion of the tantalum film 16 exposed from the openingportion 18 x in the first resist film 18 is oxidized by the first anodicoxidation in the film thickness direction. Thus, a first tantalum oxidefilm (Ta₂O₅ film) 16 a is formed. For example, the core substrate 10 onwhich the tantalum film 16 is formed is dipped into an almost 0.01%sodium citrate solution used as the electrolysis solution, and then thetantalum film 16 is connected to the anode to supply an electriccurrent. In the first anodic oxidation step, a voltage is applied up to300 V in a constant current mode, and then the voltage is applied in aconstant voltage mode until a current value comes up to a 10% value ofan initial current after the voltage reached 300 V. As a result, thefirst tantalum oxide film 16 a of almost 450 nm film thickness isformed. The first tantalum oxide film 16 a is used later as a firstdielectric film of a first capacitor. Then, the first resist film 18 isremoved.

In the anodic oxidation step, following reactions occur in the anode,the cathode, and the electrolysis solution and the anode (tantalum film)is oxidized.

-   -   Electrolysis solution: 5H₂O→10H⁺+5O²⁻    -   Anode: 2Ta+5O²⁻→Ta₅O₂₊₁₀e⁻    -   Cathode: 10H⁺+10^(e−)→5H₂

In the above anodic oxidation step, the first intermediate film 14 actsas a barrier layer and prevents the underlying conductive film 12 (e.g.,copper) from diffusing into the tantalum film 16 upon oxidizing thetantalum film 16 by the anodic oxidation. Also, the first intermediatefilm 14 acts as an adhesive layer that improves adhesiveness between theconductive film 12 and the tantalum film 16.

Then, as shown in FIG. 3D, a second resist film 18 a in which theopening portion 18 x is provided in its portion, in which a seconddielectric film of a second capacitor is formed, on the tantalum film 16is formed on the tantalum film 16 and the first tantalum oxide film 16a. Then, the portion of the tantalum film 16 exposed from the openingportion 18 x in the second resist film 18 a is oxidized by the secondanodic oxidation. Thus, a second tantalum oxide film 16 b whose filmthickness is smaller than the first tantalum oxide film 16 a is formed.In the second anodic oxidation step, the second tantalum oxide film 16 bof almost 270 nm film thickness is formed by applying the voltage up to180 V in a constant current mode in the first anodic oxidation methodused to form the above first tantalum oxide film 16 a. Then, the secondresist film 18 a is removed.

Then, as shown in FIG. 3E, a third resist film 18 b in which the openingportion 18 x is provided in its portion, in which a third dielectricfilm of a third capacitor is formed, on the tantalum film 16 is formedon the tantalum film 16 and the first and second tantalum oxide films 16a, 16 b. Then, the portion of the tantalum film 16 exposed from theopening portion 18 x in the third resist film 18 b is oxidized by thethird anodic oxidation. Thus, a third tantalum oxide film 16 c whosefilm thickness is smaller than the second tantalum oxide film 16 b isformed. In the third anodic oxidation step, the third tantalum oxidefilm 16 c of almost 90 nm film thickness is formed by applying thevoltage up to 60 V in a constant current mode in the first anodicoxidation method used to form the above first tantalum oxide film 16 a.Then, the third resist film 18 b is removed.

With the above, as shown in FIG. 3F, the first, second, and thirdtantalum oxide films 16 a, 16 b, 16 c, film thicknesses of which aredifferent mutually, are formed on predetermined portions of the tantalumfilm 16 respectively.

In the present embodiment, the tantalum film 16 is formed on the overallsurface, then the resist film 18 in which the opening portion 18 x isprovided in the predetermined portion is patterned, and then thetantalum film 16 exposed from the opening portion 18 x is oxidized inthe film thickness direction to form the first tantalum oxide film 16 a.Then, the first, second, and third tantalum oxide films 16 a, 16 b, 16 cwhose film thickness is different respectively are formed on differentportions of the tantalum film 16 respectively by repeating these steps.In addition, a plurality of tantalum oxide films (the dielectric film)whose film thickness is different respectively can be easily formed byadjusting the applied voltage in the anodic oxidation step.

In this case, like the above anodic oxidation method, it is preferablethat first the tantalum oxide film whose film thickness is thick shouldbe formed by applying a high voltage and then the tantalum oxide filmwhose film thickness is thin should be formed by applying a low voltage.This is because, in the method of first forming the thin tantalum oxidefilm and then forming the thick tantalum oxide film, it is possible thatthe already-formed tantalum oxide film is further oxidized in formingthe thick tantalum oxide film by the high-voltage anodic oxidation tocause a variation in the film thickness in the case where the defect isgenerated in the resist film.

In the above example, three tantalum oxide films 16 a, 16 b, 16 c(dielectric films) each having the different film thickness are formed.N pieces of dielectric films having the different film thicknessmutually may be formed by repeating a series of steps n times (where nis an integer of 2 or more). Also, various valve metal oxide film may beformed as the dielectric film by oxidizing other valve metal films.

Then, as shown in FIG. 3G, a second intermediate film 20 is formed byforming a Ti film or a chromium (Cr) film on an upper surface of astructure in FIG. 3F. The second intermediate film 20 is formed toimprove the adhesiveness between the tantalum oxide films 16 a, 16 b, 16c and the upper electrode formed later.

Then, as shown in FIG. 3H, metal film patterns 22 are formed on thesecond intermediate film 20. The metal film patterns 22 are formed bythe semi-additive method, for example. In more detail, a seed Cu film(not shown) is formed on the second intermediate film 20, and then aresist film (not shown) in which opening portions in which the upperelectrode is formed are provided is formed on the seed Cu film. Then, Cufilm patterns are formed in the opening portions in the resist film bythe electroplating utilizing the seed Cu film as the platingpower-supply layer. Then, the resist film is removed, and then the metalfilm patterns 22 are obtained by etching the seed Cu film while usingthe Cu film patterns as a mask.

Then, as shown in FIG. 3I, capacitor upper electrodes 23 each consistingof the second intermediate film 20 and the metal film pattern 22 areobtained by etching the second intermediate film 20 while using themetal film patterns 22 as a mask. The capacitor upper electrodes 23 arepatterned on the tantalum oxide films 16 a, 16 b, 16 c in such a mannerthat respective contact areas to a plurality of tantalum oxide films 16a, 16 b, 16 c are set identical.

Then, as shown in FIG. 3J, in order to obtain predetermined lowerelectrodes, a resist film (not shown) is patterned on an upper surfaceof a structure in FIG. 3I, then the tantalum film 16, the firstintermediate layer 14, and the conductive film 12 are etched by usingthe resist film as a mask, and then the resist film is removed. Thus,lower electrodes 15 each consisting of the conductive film 12, the firstintermediate layer 14, and the tantalum film 16 are formed. At thistime, the lower electrode 15 is formed in a state that the upper surfaceof the tantalum film 16 is exposed. Then, the core substrate 10 is cutto get a predetermined number of capacitors.

With the above, a capacitor device 1 of the present embodimentconstructed by a first capacitor C1, a second capacitor C2, and a thirdcapacitor C3 is manufactured.

In the present embodiment, a mode in which three capacitors in which thefilm thicknesses of the tantalum oxide films (dielectric films) aredifferent mutually are formed is exemplified. The number of thecapacitors is not particularly limited, and n pieces (where n is aninteger of 2 or more) of capacitors in which the film thicknesses of thedielectric films are different mutually to accord with thecharacteristics of the decoupling capacitor device may be formed. Also,the capacitors having same film thicknesses of the dielectric films andequal electrostatic capacities may be mixed among a plurality ofcapacitors.

In the capacitor device 1 of the present embodiment, upper surfaces ofthe upper electrodes 23 of respective capacitors C1, C2, C3 in FIG. 3Jact as a power-supply connecting portion 23V that is connected to thepower-supply line (+) of the circuit substrate, and the upper surfacesof the tantalum films 16 of the lower electrodes 15 act as a groundconnecting portion 23G that is connected to the ground line (−) of thecircuit substrate.

In the capacitor device 1 of the present embodiment, as shown in FIG.3J, the first capacitor C1, the second capacitor C2, and the thirdcapacitor C3 are formed on the core substrate 10 as one chip. The firstcapacitor C1 consists of the lower electrode 15, the first tantalumoxide film 16 a, and the upper electrode 23. The second capacitor C2consists of the lower electrode 15, the second tantalum oxide film 16 bwhose film thickness is smaller than the first tantalum oxide film 16 a,and the upper electrode 23. Also, the third capacitor C3 consists of thelower electrode 15, the third tantalum oxide film 16 c whose filmthickness is smaller than the second tantalum oxide film 16 b, and theupper electrode 23.

In this manner, the film thicknesses of respective tantalum oxide films16 a, 16 b, 16 c (dielectric films) are set differently mutually inrespective capacitors C1, C2, C3, and thus the electrostatic capacitiesof respective capacitors C1, C2, C3 are set differently mutually. Also,the areas of the upper electrodes 23, which contact the tantalum oxidefilms 16 a, 16 b, 16 c (areas of the portions of the dielectric filmsconstituting the capacitors), are formed equal to each other, and thusthe inductances of respective capacitors C1, C2, C3 are set identically.

FIG. 4 is a diagram showing an equivalent circuit when the capacitordevice according to the first embodiment of the present invention isapplied to the decoupling capacitor. FIG. 5 is a view showing theimpedance characteristic of the capacitor device in FIG. 4.

As shown in FIG. 4, in the capacitor device 1 of the present embodiment,respective capacitors C1, C2, C3 of the capacitor device 1 are connectedin parallel between the power-supply line and the ground line of thecircuit substrate on which the load (LSI) is mounted.

The impedance characteristics of the capacitor device 1 of the presentembodiment are shown in FIG. 5, wherein curves indicated by solid linesshow individual impedance characteristics of the capacitors C1, C2, C3respectively. The electrostatic capacities of respective capacitors C1,C2, C3 are set at this time to satisfy relationships of C1+C2+C3=90 nFand C1=3C2=5C3. The electrostatic capacity of C1 is 10 nF, and each ESRof respective capacitors C1, C2, C3 is 10 mΩ and each ESL is 50 pH.

As shown in FIG. 5, it is appreciated that resonance frequencies areshifter mutually by changing the electrostatic capacities of respectivecapacitors C1, C2, C3. The impedance characteristic of the decouplingcapacitor C1,2,3, which is constructed by connecting respectivecapacitors C1, C2, C3 in parallel, of the present embodiment isindicated by a broken line. A frequency range Y in which the impedanceis reduced smaller than 10 mΩ or less is 80 to 250 MHz.

By way of comparison the impedance characteristic of the decouplingcapacitor C₁,₂,₃, which is constructed by connecting three capacitorshaving the same electrostatic capacity shown in FIG. 1 in parallel, isindicated by a chain line in FIG. 5. As described above, a frequencyrange X in which the impedance is reduced smaller than 10 mΩ or less is90 to 180 MHz.

In this way, the low impedance can be given in a wide frequency band byconnecting a plurality of capacitors each having the differentelectrostatic capacity in parallel.

In the present embodiment, since the resonance frequencies of thecapacitors are shifted by changing the electrostatic capacities ofrespective capacitors C1, C2, C3, the impedance can be lowed over a widefrequency band. In this case, the resonance frequency of the capacitordepends on not only the electrostatic capacity but also the inductance.

In the method of changing the electrostatic capacity of each capacitorby changing the area of the dielectric film constituting the capacitor,unlike the present embodiment, the inductance is also changed betweenrespective capacitors. Therefore, the impedance reduction must beattained while taking account of the electrostatic capacity and theinductance and thus the electrical design becomes complicated.

However, in the present embodiment, as described above, the areas of theportions of the dielectric films constituting the capacitors are setidentically among respective capacitors C1, C2, C3, nevertheless theelectrostatic capacity of each capacitor is changed by the filmthickness of the dielectric film. Therefore, the inductance can be setidentically among respective capacitors C1, C2, C3.

As a result, in the present embodiment, there is no necessity for takingchanges of the inductances of respective capacitors C1, C2, C3 intoconsideration, and only the change of the electrostatic capacity may beconsidered. In addition, the resonance frequency of the capacitor hassuch a characteristic that such frequency changes in inverse proportionto the electrostatic capacity.

From the above explanation, in the capacitor device 1 of the presentembodiment, the electrical design may be conducted to attain theimpedance reduction in a wide frequency band while considering only theelectrostatic capacity. Therefore, such electrical design can be madeextremely easy.

Next, a variation of the capacitor device of the present embodiment willbe explained hereunder. In the above embodiment, as shown in FIG. 3J,the upper electrodes 23 are patterned respectively such that the uppersurfaces of the tantalum films 16 of the lower electrodes 15 inrespective capacitors C1, C2, C3 are exposed collectively. In this case,one terminal is connected to the power-supply connecting portion 23V ofthe upper electrode 23 and the ground connecting portion 23G of thelower electrode 15 respectively.

As shown in FIG. 6 and FIG. 7, in a capacitor device 1 a in thevariation of the present embodiment, four lower electrodes 15 are formedon the core substrate 10 respectively, and first to fourth tantalumoxide films 16 a to 16 d that are formed by applying the anodicoxidation to the tantalum films to have a different film thicknessrespectively are formed into patterns on the lower electrodes 15. Then,the upper electrode 23 is formed on the first to fourth tantalum oxidefilms 16 a to 16 d respectively. In this way, the first to fourthcapacitors C1, C2, C3, C4 are arranged on the core substrate 10respectively.

A plurality of opening portions 23 a are formed (two opening portionsare formed every capacitors C1 to C4 in an example in FIG. 6 and FIG. 7)in predetermined portions of the upper electrodes 23 and the tantalumoxide films 16 a to 16 d in the capacitors C1 to C4 respectively. Theupper surface of the lower electrode 15 is exposed from bottom portionsof the opening portions 23 a. Then, portions of the lower electrodes 15exposed from a plurality of opening portions 23 a act as the groundconnecting portion 23G (−) respectively. Also, a plurality ofpower-supply connecting portions 23V (+) are defined on the uppersurface of the upper electrode 23 as many as a plurality of groundconnecting portions 23G on the lower electrodes 15.

In this case, the first and second intermediate layers are omitted fromillustrations in FIG. 6 and FIG. 7. As the lower electrode 15 exposedfrom the bottom portions of the opening portions 23 a, any film (thetantalum film 16, the first intermediate film 14, or the conductive film12) constituting the lower electrode may be employed.

In the case where the above variation is employed, the inductances inrespective capacitors C1 to C4 can be reduced uniformly since aplurality of terminals are connected to the upper electrodes 23 and thelower electrode 15 respectively. Thus, the impedance can be furtherreduced in the capacitor device 1 a in the variation.

Next, an example of an electronic parts packaging structure in which thecapacitor device 1 according to the present embodiment is built as thedecoupling capacitor will be explained hereunder. FIGS. 8A to 8H aresectional views showing a method of manufacturing an electronic partspackaging structure in which the capacitor device according to the firstembodiment of the present invention is built.

First, as shown in FIG. 8A, a base substrate 30 having a packaging areaM, on which the foregoing capacitor device 1 is mounted, in its centerportion is prepared. It is preferable that a glass-epoxy substrateshould be used as the base substrate 30. Through holes 30 x are providedin the base substrate 30, and a through electrode 31 made of conductorsuch as Cu, or the like is filled in the through holes 30 xrespectively. A plurality of through electrodes 31 in the base substrate30 constitute power-supply lines V, ground lines G, and signal lines Srespectively.

Then, as shown in FIG. 8B, the above capacitor device 1 is adhered tothe packaging area M of the base substrate 30 via an adhesive layer (notshown) in a state that its surface on which the capacitors are formed isdirected upward. Then, as shown in FIG. 8C, a first interlayerinsulating film 34 is formed on both surfaces of the base substrate 30respectively by pasting a resin film onto the surfaces, or the like.Thus, the capacitor device 1 is buried in the first interlayerinsulating film 34. Then, predetermined portions of the first interlayerinsulating film 34 on the upper electrodes 23, the lower electrodes 15,and the through electrodes 31 of the capacitor device 1 are processed bythe laser, or the like, and thus first via holes 34 x are formed. Also,the first via holes 34 x are formed in the first interlayer insulatingfilm 34 on the through electrodes 31 on the back surface side of thebase substrate 30.

Then, as shown in FIG. 8D, first wiring patterns 36 connected to theupper electrodes 23, the lower electrodes 15, and the through electrodes31 of the capacitor device 1 via the first via holes 34 x respectivelyare formed on the first interlayer insulating film 34. At this time, theupper electrodes 23 of the capacitor device 1 are connected electricallyto the power-supply lines V of the base substrate 30 via the firstwiring patterns 36 respectively. Then, the first wiring patterns 36connected to the through electrodes 31 in the base substrate 30 via thefirst via holes 34 x respectively are also formed on the firstinterlayer insulating film 34 on the back surface side of the basesubstrate 30.

Then, as shown in FIG. 8E, a second interlayer insulating film 34 a forcoating the first wiring patterns 36 on both surface sides of the basesubstrate 30 is formed respectively. Then, second via holes 34 y areformed in predetermined portions of the second interlayer insulatingfilm 34 a on the first wiring patterns 36 on both surface sides of thebase substrate 30 respectively. Then, as also shown in FIG. 8E, secondwiring patterns 36 a connected to the first wiring patterns 36 via thesecond via holes 34 y on both surface sides of the base substrate 30 areformed on the second interlayer insulating film 34 a respectively. As aresult, the lower electrodes 15 of the capacitor device 1 are connectedelectrically to the ground lines G in the base substrate 30 via thefirst and second wiring patterns 36, 36 a respectively.

Then, as shown in FIG. 8F, the above processes are repeated. Thus, thirdwiring patterns 36 b connected to the second wiring patterns 36 a onboth surface sides of the base substrate 30 via third via holes 34 zformed in third interlayer insulating films 34 b respectively are formedon the third interlayer insulating films 34 b respectively.

At this time, power-supply connecting portions 36V are defined inpredetermined portions of the upper electrodes 23 of the capacitordevice 1 and the third wiring patterns 36 b connected to thepower-supply lines V of the base substrate 30. Also, ground connectingportions 36G are defined in predetermined portions of the lowerelectrodes 15 of the capacitor device 1 and the third wiring patterns 36b connected to the ground lines G of the base substrate 30. In addition,signal connecting portions 36S are defined in predetermined portions ofthe third wiring patterns 36 b connected to the signal lines S of thebase substrate 30. Also, the power-supply connecting portions 36V, theground connecting portions 36G, and the signal connecting portions 36Sare defined in the third wiring patterns 36 b exposed on the backsurface side of the base substrate 30.

Then, as shown in FIG. 8G, a solder resist film 38 in which openingportions 38 x are provided on the power-supply connecting portions 36V,the ground connecting portions 36G, and the signal connecting portions36S of the third wiring patterns 36 b on both surface sides of the basesubstrate 30 is formed on both surfaces of the structure in FIG. 8Frespectively. Then, a Ni/Au layer (not shown) is selectively formed onthe power-supply connecting portions 36V, the ground connecting portions36G, and the signal connecting portions 36S on both surface sides of thebase substrate 30 by the electroless plating respectively.

Then, as shown in FIG. 8H, an electronic parts 40 (a semiconductor chip,or the like) having bumps 40 a thereon is prepared. The bumps 40 a ofthe electronic parts 40 are flip-chip connected to respective connectingportions 36V, 36G, 36S (FIG. 8) of the third wiring patterns 36 b on theupper surface side of the base substrate 30.

Then, bumps 42 are mounted onto respective connecting portions 36V, 36G,36S (FIG. 8) of the third wiring patterns 36 b on the back surface sideof the base substrate 30.

With the above, an electronic parts packaging structure 2 in which thecapacitor device 1 of the present embodiment is built is completed.

As shown in FIG. 8H, in the circuit substrate of the electronic partspackaging structure 2 in the present embodiment, the interlayerinsulating films 34 to 34 b and the wiring patterns 36 to 36 b arestacked alternately on both surfaces of the base substrate 30 in whichthe through electrodes 31 are provided, and then the wiring patterns 36to 36 b are connected mutually via the via holes 34 x to 34 z providedin the interlayer insulating films 34 to 34 b. Then, the capacitordevice 1 is mounted on the base substrate 30 in a state that such deviceis buried in the first interlayer insulating film 34.

Then, with reference to FIG. 8H together with the above equivalentcircuit in FIG. 4, the upper electrodes 23 of three capacitors C1, C2,C3 of the capacitor device 1 are connected to the power-supply lines Vin the base substrate 30 via the first wiring patterns 36 respectively.Also, the lower electrodes 15 of three capacitors C1, C2, C3 areconnected to the ground lines G of the circuit substrate via the firstand second wiring patterns 36, 36 a respectively.

In addition, the electronic parts 40 is packaged over the capacitordevice 1 that is built in the circuit substrate. The bumps 40 a of theelectronic parts 40 are connected to the power-supply connectingportions 36V and the ground connecting portions 36G of the third wiringpatterns 36 b, which are connected to the upper electrodes 23(power-supply lines) and the lower electrodes 15 (ground lines) of thecapacitor device 1 respectively, and also connected to the signalconnecting portions 36S of the third wiring patterns 36 b, which areconnected to the signal lines in the circuit substrate.

In this fashion, respective capacitors C1, C2, C3 constituting thecapacitor device 1 are connected in parallel between the power-supplyline and the ground line connected from the circuit substrate to theelectronic parts 40.

Then, in the electronic parts packaging structure 2 of the presentembodiment, the high-frequency current (high-frequency noise) generatedfrom the electronic parts 40 is exhausted into the ground line G to goround the capacitor device 1 that is arranged directly under theelectronic parts 40. Also, even though a voltage variation is caused inthe electronic parts 40 due to a switching operation of the electronicparts 40, a voltage variation in the power-supply terminal portions ofthe electronic parts 40 can be suppressed by an action of the capacitordevice 1.

In the capacitor device 1 in the present embodiment, since the lowimpedance can be derived over a wide frequency band, as described above,the performance as the decoupling capacitor can be improved.

Also, in the capacitor device 1 in the present embodiment, since aplurality of capacitors each having the different electrostatic capacityare incorporated into one chip, it is unnecessary to package a pluralityof individual capacitor parts whose electrostatic capacities aredifferent. Therefore, a packaging cost can be reduced and also apackaging density can be improved.

In addition, a thickness of the capacitor device 1 in the presentembodiment can be reduced by reducing a thickness of the core substrate10, and can also be arranged immediately under the electronic parts 40.Therefore, the parasitic inductance can be largely reduced. As a result,an effect of suppressing a variation in the power-supply voltage appliedto the high-speed operated electronic parts and also reducing thehigh-frequency noise can be enhanced.

Second Embodiment

FIGS. 9A to 9C are sectional views showing a method of manufacturing acapacitor device according to a second embodiment of the presentinvention. A difference of the second embodiment from the firstembodiment is that a method of forming the dielectric film is different.Detailed explanation of the same steps as those in the first embodimentwill be omitted herein.

First, as shown in FIG. 9A, the conductive film 12 is formed on the coresubstrate 10. Then, a first dielectric film pattern 16 x is formed inthe portion of the conductive film 12 in which the dielectric film ofthe first capacitor is formed. As a method of forming the firstdielectric film pattern 16 x, there is a lift-off method, for example.More particularly, first a resist film (not shown) having an openingportion in a predetermined portion is patterned. Then, a dielectric filmsuch as a tantalum oxide film, or the like is formed on the resist filmand in the opening portion by the sputtering method, or the like. Then,the dielectric film formed in the opening portion in the resist film isselectively left by releasing the resist film, and thus the firstdielectric film pattern 16 x is obtained.

Then, similar steps are carried out after the position of the openingportion in the resist film and the film thickness of the dielectric filmare changed respectively. Thus, a second dielectric film pattern 16 yand a third dielectric film pattern 16 z, each having a different filmthickness from the first dielectric film pattern 16 x, are formed inseriatim. A plurality of dielectric film patterns each having thedifferent film thickness can be formed in different areas of theconductive film 12 respectively by repeating the lift-off steppredetermined times.

Alternately, the dielectric material such as PZT (Pb(Zr,Ti)O₃), or thelike may be formed by employing a method of patterning the gel used inthe sol-gel method by means of the printing using a metal mask, in whichthe opening portion is provided in the predetermined portion, and thensintering the gel. In this case, a plurality of dielectric film patternseach having the different film thickness can be formed by repeating thesimilar steps the predetermined number of times while using a pluralityof metal masks that have different thickness and position of the openingportion respectively.

Then, as shown in FIG. 9B, the upper electrode 23 is patterned on thefirst, second, and third dielectric film patterns 16 x, 16 y, 16 zrespectively. Then, as shown in FIG. 9C, the lower electrodes 15 areformed by patterning the conductive film 12. Then, the core substrate 10is cut to get the predetermined capacitors.

As a result, like the first embodiment, a capacitor device 1 bconstructed by the first, second, and third capacitor C1, C2, C3 inwhich the film thicknesses of the dielectric film are different mutuallycan be manufactured.

The capacitor device 1 b of the second embodiment can achieve thesimilar advantages to the first embodiment. Also, in the capacitordevice 1 b of the second embodiment, a variation and a modification canbe applied similarly to the first embodiment, and also such capacitordevice can be applied to the similar decoupling capacitor to the firstembodiment.

1. A capacitor device comprising: a substrate; a plurality of lowerelectrodes formed on the substrate; a plurality of dielectric filmsformed on the plurality of lower electrodes respectively in a state thatthe dielectric films are separated mutually; and upper electrodes formedon the plurality of dielectric films respectively; wherein a pluralityof capacitors each composed of the lower electrode, the dielectric film,and the upper electrode are arranged on the substrate respectively, andeach of the dielectric films in the plurality of capacitors has adifferent film thickness.
 2. A capacitor device according to claim 1,wherein areas of portions of the dielectric films constituting thecapacitors are set identically in the plurality of capacitors.
 3. Acapacitor device according to claim 1, wherein the dielectric films aremade of a metal oxide film that is formed by applying anodic oxidationto a valve metal film from an upper surface along a film thicknessdirection, and the lower electrodes contain the valve metal film.
 4. Acapacitor device according to claim 3, wherein the valve metal film is atantalum film, an aluminum film, or a titanium film.
 5. A capacitordevice according to claim 3, wherein areas in which the metal oxide filmis not formed are left on upper surfaces of patterns of the valve metalfilm, and the upper electrodes are formed to expose upper surfaces ofthe areas, in which the metal oxide film is not formed, of the patternsof the valve metal film.
 6. A capacitor device according to claim 3,wherein a plurality of opening portions are provided in predeterminedportions of the upper electrodes and the metal oxide film, and the lowerelectrode is exposed from bottom portions of the opening portions.
 7. Acapacitor device according to claim 1, wherein the substrate is made ofmaterial that is selected from a group consisting of silicon, glass,ceramic, and resin.
 8. A capacitor device according to claim 1, whereina thickness of the substrate is 50 μm or less.
 9. An electronic partspackaging structure comprising: a circuit substrate having apower-supply line and a ground line; the capacitor device set forth inclaims 1 and packaged on the circuit substrate, a plurality ofcapacitors of the capacitor device being connected in parallel betweenthe power-supply line and the ground line; and an electronic partspackaged over the capacitor device and connected between thepower-supply line and the ground line.
 10. An electronic parts packagingstructure according to claim 9, wherein upper electrodes of theplurality of capacitors are connected to the power-supply linerespectively, and lower electrodes of the plurality of capacitors areconnected to the ground line respectively.
 11. An electronic partspackaging structure according to claim 10, wherein the capacitor deviceis set forth in claim 5, and upper surfaces of the valve metal filmsconstituting the lower electrodes are connected to the ground linerespectively.
 12. A method of manufacturing a capacitor devicecomprising the steps of: forming a conductive film on a substrate;forming a plurality of dielectric film patterns each having a differentfilm thickness in a plurality of different areas on the conductive filmrespectively; forming upper electrodes on the plurality of dielectricfilm patterns respectively; and forming a plurality of lower electrodesrespectively by patterning the conductive film to obtain a plurality ofcapacitors constructed by the lower electrodes, the dielectric filmpatterns, and the upper electrodes on the substrate.
 13. A method ofmanufacturing a capacitor device comprising the steps of: forming aconductive film on a substrate; forming a valve metal film on theconductive film; forming a plurality of dielectric films each having adifferent film thickness in different areas of the valve metal filmrespectively by repeating n times (n is an integer of 2 or more) thestep of forming a resist film, in which opening portions are provided inpredetermined portions, on the valve metal film and the step of forminga dielectric film made of a metal oxide film by oxidizing the valvemetal film exposed from the opening portions in a film thicknessdirection by means of anodic oxidation; forming upper electrodes on theplurality of dielectric films respectively; and forming a plurality oflower electrodes composed of the valve metal film and the conductivefilm respectively by patterning the valve metal film and the conductivefilm to obtain a plurality of capacitors constructed by the lowerelectrodes, the dielectric films, and the upper electrodes on thesubstrate.
 14. A method of manufacturing a capacitor device according toclaim 12, wherein, in the step of forming the upper electrodes, contactareas of the upper electrodes to the dielectric film are set identicallyamong the plurality of capacitors.
 15. A method of manufacturing acapacitor device according to claim 13, wherein, in the step of formingthe upper electrodes, contact areas of the upper electrodes to thedielectric film are set identically among the plurality of capacitors.16. A method of manufacturing a capacitor device according to claim 13,wherein, in the step of forming the plurality of dielectric films eachhaving the different film thickness by the anodic oxidation, filmthicknesses of the plurality of dielectric films are controlled by anapplied voltage in the anodic oxidation, and the plurality of dielectricfilms are formed sequentially in order of larger film thickness.
 17. Amethod of manufacturing a capacitor device according to claim 13,wherein the valve metal film is a tantalum film, an aluminum film, or atitanium film.